package libember.s101;

import java.util.Iterator;

/**
 * This class contains the value table of a 16 bit crc and provides methods to
 * compute the crc. Since this class is internal its method do not perform any
 * argument evaluation, but assume the arguments are valid.
 */
final class Crc16 {
	private final static int[] table = new int[] { 0x0000, 0x1189, 0x2312,
			0x329B, 0x4624, 0x57AD, 0x6536, 0x74BF, 0x8C48, 0x9DC1, 0xAF5A,
			0xBED3, 0xCA6C, 0xDBE5, 0xE97E, 0xF8F7, 0x1081, 0x0108, 0x3393,
			0x221A, 0x56A5, 0x472C, 0x75B7, 0x643E, 0x9CC9, 0x8D40, 0xBFDB,
			0xAE52, 0xDAED, 0xCB64, 0xF9FF, 0xE876, 0x2102, 0x308B, 0x0210,
			0x1399, 0x6726, 0x76AF, 0x4434, 0x55BD, 0xAD4A, 0xBCC3, 0x8E58,
			0x9FD1, 0xEB6E, 0xFAE7, 0xC87C, 0xD9F5, 0x3183, 0x200A, 0x1291,
			0x0318, 0x77A7, 0x662E, 0x54B5, 0x453C, 0xBDCB, 0xAC42, 0x9ED9,
			0x8F50, 0xFBEF, 0xEA66, 0xD8FD, 0xC974, 0x4204, 0x538D, 0x6116,
			0x709F, 0x0420, 0x15A9, 0x2732, 0x36BB, 0xCE4C, 0xDFC5, 0xED5E,
			0xFCD7, 0x8868, 0x99E1, 0xAB7A, 0xBAF3, 0x5285, 0x430C, 0x7197,
			0x601E, 0x14A1, 0x0528, 0x37B3, 0x263A, 0xDECD, 0xCF44, 0xFDDF,
			0xEC56, 0x98E9, 0x8960, 0xBBFB, 0xAA72, 0x6306, 0x728F, 0x4014,
			0x519D, 0x2522, 0x34AB, 0x0630, 0x17B9, 0xEF4E, 0xFEC7, 0xCC5C,
			0xDDD5, 0xA96A, 0xB8E3, 0x8A78, 0x9BF1, 0x7387, 0x620E, 0x5095,
			0x411C, 0x35A3, 0x242A, 0x16B1, 0x0738, 0xFFCF, 0xEE46, 0xDCDD,
			0xCD54, 0xB9EB, 0xA862, 0x9AF9, 0x8B70, 0x8408, 0x9581, 0xA71A,
			0xB693, 0xC22C, 0xD3A5, 0xE13E, 0xF0B7, 0x0840, 0x19C9, 0x2B52,
			0x3ADB, 0x4E64, 0x5FED, 0x6D76, 0x7CFF, 0x9489, 0x8500, 0xB79B,
			0xA612, 0xD2AD, 0xC324, 0xF1BF, 0xE036, 0x18C1, 0x0948, 0x3BD3,
			0x2A5A, 0x5EE5, 0x4F6C, 0x7DF7, 0x6C7E, 0xA50A, 0xB483, 0x8618,
			0x9791, 0xE32E, 0xF2A7, 0xC03C, 0xD1B5, 0x2942, 0x38CB, 0x0A50,
			0x1BD9, 0x6F66, 0x7EEF, 0x4C74, 0x5DFD, 0xB58B, 0xA402, 0x9699,
			0x8710, 0xF3AF, 0xE226, 0xD0BD, 0xC134, 0x39C3, 0x284A, 0x1AD1,
			0x0B58, 0x7FE7, 0x6E6E, 0x5CF5, 0x4D7C, 0xC60C, 0xD785, 0xE51E,
			0xF497, 0x8028, 0x91A1, 0xA33A, 0xB2B3, 0x4A44, 0x5BCD, 0x6956,
			0x78DF, 0x0C60, 0x1DE9, 0x2F72, 0x3EFB, 0xD68D, 0xC704, 0xF59F,
			0xE416, 0x90A9, 0x8120, 0xB3BB, 0xA232, 0x5AC5, 0x4B4C, 0x79D7,
			0x685E, 0x1CE1, 0x0D68, 0x3FF3, 0x2E7A, 0xE70E, 0xF687, 0xC41C,
			0xD595, 0xA12A, 0xB0A3, 0x8238, 0x93B1, 0x6B46, 0x7ACF, 0x4854,
			0x59DD, 0x2D62, 0x3CEB, 0x0E70, 0x1FF9, 0xF78F, 0xE606, 0xD49D,
			0xC514, 0xB1AB, 0xA022, 0x92B9, 0x8330, 0x7BC7, 0x6A4E, 0x58D5,
			0x495C, 0x3DE3, 0x2C6A, 0x1EF1, 0x0F78, };

	/**
	 * Computes the crc based on a current crc and an input byte.
	 * 
	 * @param crc
	 *            The initial or current crc value.
	 * @param input
	 *            The byte to append to the crc.
	 * @return The new crc value.
	 */
	public static int sample(int crc, int input) {
		return 0xFFFF & ((crc >>> 8) ^ table[(crc ^ input) & 0xFF]);
	}

	/**
	 * Computes a crc for a collection of bytes.
	 * 
	 * @param crc
	 *            The initial or current crc value.
	 * @param input
	 *            The collection to compute the crc for.
	 * @return The crc value.
	 */
	public static int sample(int crc, Iterator<Integer> input) {
		while (input.hasNext()) {
			crc = sample(crc, input.next());
		}
		return crc;
	}
}
